Electric control and indicating circuits



Sept. 20, 1938. B. D. BEDFORD ELECTRIC CONTROL AND INDICATING CIRCUITS Filed Jan. 30, 1956 Q@ www x kh.

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Patented Sept. 20, 1938 ELECTRIC CoN'moL AND INDICATINC.

CIRCUIT Burnice D. Bedford, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application January 30, 1936, Serial No. 61,528

Claims.

My invention relates to electric circuits and more particularly to indicating and control systems for electric valve circuits.

Where a plurality of elements in mechanical 5 and electrical systems are intended to operate in a predetermined mode or in accordance with certain operating conditions, it is sometimes desirable to provide electric signaling systems to afford an indicationwhen the elements depart from a predetermined mode of operation and to aiord an indication of the nature of the irregular operation which has occurred. In electric translating circuits which employ electric valves, it is desirable in many instances to provide auxiliary control and indicating systems to indicate a condition of operation of the electric translating circuit. Particularly in power systems where electrical energy is transmitted by means of electric valves, lt is frequently desirable to provide indicating systems or` control systems which are responsive to abnormal operation of the electric system to control the system in response to such irregular operation, or to provide an indication when the system has departed from a predetermined mode of operation. It is desirable that these control and indicating systems be inherently capable of precisely and accurately responding to predetermined operating conditions and it is also desirable that these circuits be readily adaptable to electric translating systems generally, without necessitating material change or alteration in the apparatus employed in the electric system and without interfering with the manner in which the system operates.

An object of my invention is to provide improved control and indicating systems for electric valve translating circuits which function in response to a departure from a predetermined mode or manner of operation of the translating circuit.

Another object of my invention is to provide an improved control and indicating circuit for electric valve translating apparatus which functions to control an associated circuit or to afford an indication when the electric valves of the translating circuit conduct at any time other than during predetermined intervals.

A further object of my invention is to provide an indicating system for indicating which fault of predetermined different kinds of faults has been the first to occur in an electric valve translating system.

In accordance with the illustrated embodiment of my invention a control and indicating system is provided for electric valve translating circuits.

The system hereinafter described may comprise a circuit for affording an indication of the valve of a plurality of electric valves which is' the first to lose control, that is, the first valve to conduct at any time other than during predetermined intervals or to afford an indication when the valves begin to conduct at instants other than predetermined instants in the cycle of operation. The control and indicating system also may comprise a circuit to indicate which electric valve of a plurality of electric valves is the iirst to fail to conduct within a predetermined interval or period, or to indicate the iirst valve which fails to become conductive at predetermined instants in the cycle of operation. A reverse current or arcback indicating circuit is also included in the system to indicate which valve of a plurality of electric valves has been the iirst to experience a reverse current or arc-back condition. To provide a means for indicating which of the above types of irregular or abnormal operation has been the iirst to occur, an additional indicating circuit is provided to be responsive to and to indicate which of the above mentioned indicating circuits has been the rst to respond to irregular operation.

For a better understanding of my invention, together with other and further objects thereof, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the single figure of the drawing, which is a diagrammatic representation of an embodiment of my invention as applied to an electric valve translating system for transmitting energy between a three phase alternating current circuit and a direct current load circuit. Electrical energy is transmitted from a three phase alternating current circuit I to the direct current load circuit 2 through a transformer 3 and electric valves 4, 5 and 6. Connected in series with the transformer 3 is a circuit interrupter 'I having an electroresponsive actuating element 8. Secondary windings 3 of the transformer 3 are connected to the electric valves 4, 5 and 6 through current responsive means, such as transformers 9, I0 and II. By means of conductors I2, I3 and I4 current responsive means, such as current transformers I5, I6 and Il, are connected in series with current directional means such as saturable reactors I8, I9 and 20, all of which are connected in series with electric'valves I, 5 and 6, respectively. The saturable reactors I8, I9 and 20 are each provided with a series winding 2|, a unidirectional saturating winding 22 and a current direction responsive winding 23.

To provide means for indicating which electric valve of valves 4, 5 and 6 is the first valve to lose control, that is, to depart from a predetermined mode or condition of operation by conducting current during intervals in which the valves are normally nonconductive, an electric circuit 24 comprising auxiliary electric valves 25, 26 and 21 is employed. Electric valves 25, 26 and 21 are associated with main electric valves 4, 5 and 6, respectively, and each is provided with an anode 26, a cathode 29 and a control electrode 36. By means of a voltage divider comprising a resistance 3i which is energized from a direct current source 32, a positive potential is impressed upon the respective anodes 26 of electric valves 25, 26 and 21 by means of a conductor 33, a resistance 34, and an inductive current responsive element 35. The cathodes 29 of electric valves 25, 26 and 21 are connected through a conductor 36 and a lamp 31 to a point of less positive potential on the resistance 3|. To control the conductivity of electric valves 25, 26 and 21 in response to a predetermined operating condition of electric valves 4, 5 and 6, a potential is impressed upon the various control electrodes 36 of these valves by suitable current responsive means such as transformers 9, I0 and Il, which are of the 'magnetic saturable type. The lower terminals of the secondary windings of current transformers 9, I0 and il are connected to the negative side of the direct current source 32 by means of a conductor 38. The upper terminals of the secondary windings of transformers 9, lli and Ii are connected to the control electrodes 39 of electric valves 25, 26 and 21. Connected in series with each of the anode circuits of electric valves 25, 26 and 21 are magnetic saturable voltage vtransformers 39, 40 and 4I, respectively, which are energized through any conventional phase shifting device 42. Connected in parallel with the secondary windings of voltage transformers 39, 40 and 4I are non-linear resistance elements 39', 40' and 4I', which function to introduce in the anode circuits of electric valves 25, 26 and 21 negative voltages of substantially peaked wave form. The non-linear resistance elements 39', 40' and 4I may be of the material disclosed and claimed in U. S. Patent No. 1,822,742 granted September 8, 1931 on an application of Karl B. McEachron and assigned to the assignee of the present application. A negative voltage is impressed upon the various control electrodes of electric valves 25, 26 and 21 by means of the conductor 38 and through the secondary windings of saturable current transformers 9, I0 and Il, respectively. An electric valve 43, preferably of the vapor electric discharge type, is connected in parallel ywith the resistance 34 and the current responsive element 35, and is also connected to the direct current source 32 by means of a conductor 44.

The operation of the loss-of-control indicator or circuit 24 will be ilrst explained by considering valves 25, 26 and 21 during normal operation of electric valves 4, 5 and 6. That is, when these valves are conducting current positive voltages will be impressed periodically upon the control electrodes 36 of electric valves 25, 26 and 21 by means of current transformersV 9, I6 and Il. By means of the phase shifting device 42, which is energized from the alternating current circuit i, the phase of the negative peaked voltages irnpressed upon the anodes 26 of electric valves 25. 26 and 21 may be adjusted relative to the positive voltages impressed upon the control electrodes 30 of these valves so that these voltages are in substantialphase coincidence. During normal operation it will be noted that as electric valves 4, 5 and 6 conduct current because of the saturation effects of transformers 6, I6 and il, a peak of positive voltage will be impressed upon the various control electrodes 36 at the beginning of the respective periods of conduction. However, since the saturable voltage transformers 36, 40 and 4l are adjusted for normal operation to impress negative potentials upon the anodes 26 of electric valves 25, 26 and 21 at precisely the instants at which the positive voltages are impressed upon the control electrodes, the electric valves 25, 26 and 21 will be maintained nonconductive.

If electric valves 4, 5 and 6 conduct current at any time other than during the predetermined periods, or begin to conduct current at any time other than the proper predetermined instants in the respective cycles of operation, it will be noted that the above mentioned phase coincidence between the voltages of transformers 39, 46 and 4I and transformers 9, ill and Il will be disturbed. For example, if electric valve 4 conducts at any time other than during the predetermined interval or if electric valve 4 fails to become conductive at the predetermined instants in accordance with its predetermined mode of operation, electric valve 25 will be rendered conductive by virtue of the positive voltage impressed upon the control electrode 3l by current transformer 9. Upon being rendered conductive, electric valve 25 will conduct current to energize the current responsive element 35 from the direct current source 32 and resistance 3i through resistance 34, conductor 33, secondary winding of .transformer 39, indicating lamp 31 and conductor 36. Electric valve 43, which is connected to the positive side of the direct current source 32 through conductor 44, will impress upon the respective anodes 26 of electric valves 25, 26 and 21 a potential more positive than that eii'ective prior to conduction by electric valve 25. The effect of such operation, if the additional positive voltage impressed upon the anodes is of suiilcient value, will be to render ineifective the alternating negative potentials of peaked wave form impressed upon the various anode circuits by means of the voltage transformers 39, 46 and 4i. In other words, after one of electric valves 25, 26 and 21 has been rendered conductive, it will be maintained conductive until the direct current source 32 is disconnected from the circuit 24 by means of a switch 45. The lamp 31, of course, will be energized in response to energization of the indicating circuit 24 to afford an indication that one of the electric valves has lost control or failed to operate according to a predetermined mode of operation, and the electric valve of the group of valves 25, 26 and 21 which is conductive will indicate which of the main electric valves 4, 6 and 6 has been the ilrst to lose control. It electric valves 25, 25 and 21 are of the vapor electric discharge type, the characteristic glow will serve .to indicate that the electric valve is conductive.

If electric valves oi' the highvacuum type are utilized, an indicating device responsive to an electrical condition oi the electric valve or associated circuit may be employed to indicate tlr fact that the electric valve is conductive.

It should be understood that after one of the electric valves of the group comprising valves 25, 25 ,and 21 is rendered conductive, the negative bias voltage impressed upon the control electrodes 30 of the remaining valves is increased to a value less positive than the critical value for these valves so that the remaining valves will be maintained non-conductive even though there are subsequent irregularities in the operation of the main electric valves. This increase in negative bias voltage is occasioned by the increased current flow through the resistor 5I.

Although in the above explanation of the operation of the loss-of-control circuit 24 it has been assumed that the circuit operates to afford an indication or to control the translating circuit when one of the main electric valves 4, 5 and 5 fails to become conductive at a predetermined instant in the cycle of operation, it should be further understood that my invention in its broader aspects is also applicable to those arrangements in which it is desired to provide a control or an indication when one of these main v electric valves conducts at any time other than during a predetermined interval. This variation in the manner of operation of the control and indicating circuit may be obtained by adjusting the shape of the voltage waves provided by the current transformers 9, I and II and the shape of the voltage waves provided by the transformers 39, 45 and 4I. If it is desirable to aiord an indication or to obtain circuit control when the electric valves d, and 5 conduct at any time other than during a predetermined normal or extended interval, the transformers 39, 49 and 4I may be designed to provide a negative voltage of substantially rectangular wave form having a period of suitable value to meet this requirement. In such a modication, the negative voltages impressed upon the anodes 25 of electric valves 25, 26 and 21 will be effective to maintain these valves non-conductive during predetermined intervals corresponding to and correlated with the normal periods of conduction of the main electric valves 4, 5 and 6.

To provide means for ail'ording an indication when electric valves 4, 5 and 5 fail to conduct within predetermined intervals, I provide a control and indicating circuit 45 which may be termed a failure-to-conduct circuit. This arrangement is disclosed and claimed in my copending application Serial No. 133,233 entitled Electric control and indicating circuits, filed March 26, 1937 and assigned to the assignee of the present application. The circuit 45 may comprise electric valves 41, 45 and 49,each having an anode 55, a cathode 5I vand a control electrode 52. The control valves 41, 45 and 49 are associated with main valves 4, 5 and 5, respectively, to indicate a condition of operation of the latter valves. The anodes 55 of electric valves 41, 45 and 49 have impressed thereon a positive potential from the direct current source 32 by means of a conductor 53, resistance 54,'an inductive current responsive element 55, resistance 55, conductor 51, the secondary windings 0f current responsive means I5, I5 and I1 and conductors 55. Non-linear resistances I5', I5' and I1' are connected across the secondary windings of current responsive elements I5, I5 and I1. The values of the non-linear resistances I5', I5 and I1' are chosen so that the output voltage of the current responsive means I5, I5 and I1 impressed upon the respective anodes 55 of electric valves 41, 45 and 49 are of substantially rectangular wave form having a relatively broad characteristic. An electric valve 55 of the vapor electric discharge type is connected in parallel with the serially connected resistance 55 and the current responsive element 55 to increase the posit-ive potential impressed in the associated anode circuits of control valves 41, 45 and 49 when one of these valves is rendered conductive due to the abnormal operation of the main electric valves 4, 5 and 5. The cathodes 5I of electric valves 41, 45 and 49 are connected to a relatively negative potential point of the resistance 54 by means of an indicating lamp 59 and a conductor 55. A negative potential is impressed upon the control electrodes 52 of electric valves 41, 45 and 49 from the direct current source 32 by means of a conductor 5I and secondary windings of voltage transformers 52, 53 and 54. The transformers 52, 53 and 54 are energized through a conventional phase shifting device 55 to impress positive potentials of peaked wave form on the control electrodes 52 of electric valves 41, 45 and 49 during predetermined intervals corresponding to and correlated with the normal periods or intervals of conduction of the main electric valves 4, 5 and 5.

The operation of the failure-to-conduct circuit 45 will be first explained by considering the system during normal operation of the main electric valves 4, 5 and 5, that is, when these valves are conducting current during the normal intervals and are being rendered conductive in a predetermined sequence to supply unidirectional current to the load circuit 2. For purposes of explanation, the operation of the indicating and control circuit 45 will be considered in connection with the main electric valve 4. When the electric valve 4 conducts during normal predetermined intervals, the associated control electric valve 41 will be maintained nonconductive. During the period of conduction, the current transformer I5 will impress upon the anode 50 of control valve 41 a negative voltage to render ineffective the positive voltage impressed upon the anode 50 and also to render ineffectivethe positive voltage impressed upon the control electrode 52 by means of the transformer 52. It will, therefore, be noted that the associated control valve 41 will be maintained non-conductive and the failure-to-conduct circuit 46 will not be operated.

If it be assumed that the main valve 4 fails to conduct during a predetermined interval, the positive voltage impressed upon the anode 55 of the associated control valve 41 from the direct current source 32 will be effective and the control valve 41 will be rendered conductive by the positive potential impressed upon the control electrode 52 by the transformer 52. Upon being rendered conductive, the control electric valve 41 will establish a circuit to energize the indicating lamp 59. This circuit comprises the positive terminal of the direct current source 32, conductor 53, the upper portion of resistance 54, current responsive element 55, resistance 55, conductor 51, secondary winding of current responsive means I5, conductor 55, electric valve 41,

electric valve 88 will be maintained conductive and serves the purpose of maintaining the electric valve 41 conductive to effect energization ci.'

the indicating lamp 58. thereby maintaining a continuing visual indication ci the fact that the translatingclrcuit has experienced an abnormal operating condition. If the control valves 41, 48 and 48 are of the vapor electric discharge type, the characteristic glow of the valves will serve to ailord an indication that the valve is conductive and further show that the associated main elec-v tric valve has failed to conduct during a predetermined interval. It should be understood that if it is desired, an auxiliary indicating means may be associated with each of the control valves 41, 48 and 48 and may be energized in response to the energization oi' these valves.

The failure-to-conduct circuit 48 may also be employed to indicate failure of the main electric valves 4, 5 and 8 to become conductive at predetermined instants inthe respective cycles of operation. One way in which this may be accomplished is to design the transformers 82, 88 and 84 to provide voltages of peaked wave form of predetermined duration and having substantial phase coincidence with the instants at which each of the main electric valves 4, 5 and 8 is to become conductive. In this manner it will be understood that if the main electric valves 4, 5 and 8 fail to become conductive at the proper instants, the associated control valves 41, 48 and 48 will be rendered conductive by the peak voltages supplied transformers 82, 88 and 64.

The control and indicating circuit 48 is arranged in a manner to indicate the first valve of main electric valves 4, 5 and 8 to fail to conduct within a predetermined interval or to fail to become conductive at predetermined instants in the respective cycles'of operation. After one of the electric valves 48, 41 and 48 has been rendered conductive, the other valves of this group will be maintained non-conductive by virtue of the increased negative bias voltage occasioned by the current transfer through the resistance 58, resistance 54 and the lamp 58.

An electric circuit 81 comprising'electric valves 88, 88 and 18 is employed to indicate which of the nain electric valves 4, 5 and 8 has been the first to experience a reverse current or arc-back condition. The arc-back control and indicating circuit 81 is disclosed and broadly claimed in my copending application serial No. 61,529 flied January 30, 1936, and assigned to the assignee of the present application. Control valves 88, 88 and 18 are associated with main valves 4, 5 and 8, respectively, to provide an indication of an operating condition of the latter valves. Each of the electric valves 88, 88 and 18 is provided with an anode 1I, a cathode 12, and va control electrode 18. A positive potential is impressed upon the various anodes 1I from the direct current source 82 by means of a resistance 14 through conductors 58 and 8i. A conductor 15 is utilized to connect the anodes to the positive terminal of resistance 14. To provide means responslve to the direction of current transfer through the main electric'valves 4, 5 and I, I employ saturable reactances I8, I8 and 2l, each comprising a magnetizing winding 2l connected in series with electric valves 4, l and 8 by conductors I2, I8 and I4, respectively, unidirectional magnetizing means comprising winding 22 energized from the direct current source 82 and a control winding 28. 'I'he unidirectional magnetizing windings 221are provided to saturate the reactors I8, I8 and 28 and are connected to the direct current source 82 through a conductor 1l, a resistance 18, an inductance 11, a conductor 18 and a conductor 18. The unidirectional saturating windings 22 oi the saturable reactors I8, I8 and 28 are arranged relative to the series connected magnetizing windings 2I so that these windings assist the magnetomotive forces established by the series windings 2I during normal operation of the main electric valves 4, 8 and 8.

Thek operation of the arc-back indicators 81 willbe rst considered during the normal operation of the main electric valves 4, 5 and 8. For example, if electric valve 4 conducts current in the normal direction, the associated control electric valve 88 will be maintained non-conductive by virtue of the negative potential impressed upon the control electrode 18 from the negative terminal of the direct current source 82 by means of conductor 8|, conductor 18, current directional responsive winding 23, and conductor 88. However. if the main valve 4 conducts current in the reverse direction, this reverse current flowing through the series winding'Zl will effect a change in the magnetization of the saturable reactor I8 to induce a voltage in the winding 28 to impress upon the control electrode 13 of control valve 68 a positive potential to render the latter valve conductive, thereby affording an indication that the main valve 4 has experienced an arc-back or reverse current condition. After control valve 88 has been rendered conductive, the negative potential impressed upon the control electrodes of control valves 88 and 10 will be increased to a value less positive than the critical control potential for the.particular valve employed, so that these valves will not be rendered conductive even though a subsequent arc-back condition obtains upon main valves 5 and 8, respectively. Upon being rendered conductive, the control valve 88 will eiect energization of the indicating lam II.

To provide a means for indicating which of the three above described types of irregular operation has been the ilrst to occur, an electric circuit 82 is employed comprising electric valves 88, 84 and 85 energizedirom the direct-current source 32, through conductors 53 and 8|, and through a resistance 86. Electric valves 83, 84 and 85are associated with indicating circuits 24, 46 and 81, respectively. The operation o f the circuit 82 is similar to the operation of the circuit 81 described above. Associated with electric valves 83, 84 and 85 are electric lamps 81, 88 and 88, respectively. The electric circuit 82 will indicate which type of failure has been the ilrst to occur since the electric valve 88 is associated with the circuit 24, the electric valve 84 is associated with the electric circuit 48 and the electric valve 85 is associated with electric circuit 81. The electro-responsive element 8 of the circuit interrupter 1 is connected in series with the electric valves 88, 84 and 85 and the associated lamps 81, 88 and 88, respectively, by means of conductors 88 and a switch 8 I. When it is'desired'to obtain only an indication of the type of failure which has been the rst to occur and when it is not desirable to control the translating circuit in response to the above described failures, the switch 9| may be operated to interrupt the circuit to the electro-responsive element 8 ot the circuit interrupter 1.

The general principles of operation of the control and indicating system diagrammatically illustrated in the single figure of the drawing may be best explained by considering the operation of the system under fault conditions of the various natures described above. If it be assumed that the electric valve 4 conducts at any time other than during a predetermined interval or fails to become conductive at predetermined instants, the electric valve 25 in the indicating circuit 24 will be rendered conductive and will be maintained conductive by the electric valve 43 to indicate that the electric valve 4 was the first electric valve to lose control. The lamp 31 will also be energized to indicate that this particular type of fault has occurred. In response to the energization of circuit 24, electric valve 83 of the priority indicating circuit 82 will be rendered conductive, effecting energization of the associated lamp 81. After electric valve 83 has been rendered conductive, the anode-cathode voltage and the control element voltages of the other electric valves of this group will be reduced below the critical voltages for the particular valves used to maintain the other valves of group 82 non-conductive. If electric valves 5 and 6 are subsequently subjected to a fault of a similar nature, that is, if these valves lose control after electric valve 4 has lost control, no indication will be afforded of these occurrences. However, if faults of a. different nature occur, such as failure to conduct within a predetermined period or an arc-back condition exists, electric circuits 46 and 61, respectively, will function to afford an indication of the rst valve to experience such condition. However, the circuit 82 will not respond to these subsequent failures inasmuch as the function of this circuit is to indicate the occurrence of the first type of failure.

As a further example of the manner in which the indicating system operates, if it be assumed that the electric valve 5 fails to conduct within a predetermined interval or fails to become conductive at predetermined times, the associated electric valve 48 in circuit 46 will be rendered conductive and the electric valve 66 will also be rendered conductive to maintain the circuit condition to afford a continuing indication that the electric valve 5 has failed to conduct within a predetermined interval. In response to this circuit operation, the indicating lamp 59 will be' energized to show that a failure of this nature has occurred in the electric valve translating circuit. In response to the operation of circuit 46, the valve 84 of group 82 will be rendered conductive to effect energization of the indicating lamp 88. In the event valves 4, 5 and 6 experience subsequently a loss of control or an arc-back condition, the electric circuits 24 and 61, respectively, will function to provide an indication of the rst electric valve to experience the particular type of fault. However, the priority indicating circuit 82 will not respond and will provide only an indication that the first type of abnormal operation to occur was the failure-to-conduct fault previously described in connection with electric valve 5.

As another example, if electric valve 6 of the translating circuit experiences an arc-back or reverse current condition, the `electric valve 'l0 of group S1 will be rendered conductive to effect energization of the indicating lamp 8l to show that this type of failure has occurred in the circuit. In responsey to this operation, valve 85 ofthe priority indicator 82 will be rendered conductive to eiect energization of indicatinglamp 88. In the manner described above, as the electric valves 4, 5 and 6 experience subsequently faults of a dii'- ferent nature, the electric circuits 24 and 48 will respond to indicate which valve was the first to experience they particular type of fault. These subsequent abnormal circuit operations will not affect the indication provided by the priority indicator 82 which is intended to indicate the ilrst typev of fault which has occurred.

It'should be understood that by operation of the switch 45 the indicating system may be reset by interrupting the potential applied to the various circuits by the source 32. In the event it is desirable to effect circuit interruption upon the occurrence of the ilrst fault, the switch 8i may be moved to the position in which electroresponsive element 8 is connected in series with the various parallel circuits of the priority indicator 82. When such a circuit connection is arranged, the various circuits, of course, will function to indicate failures in the above described manner until the electric valve translating circuit is opened by circuit interrupter While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modiiications 'as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. In combination, an electric translating cir cuit including a group ofv electric valves, means for rendering said electric valves conductive during different predetermined intervals, and a circuit for indicating the first of said electric valves to conduct current at any time other than during said intervals and including a plurality of electric valveseach having an anode, a cathode and a control electrode and each being associated with a predetermined one of said first mentioned valves, comprising means for impressing on the anodes of said second mentioned valves a positive potential, means for impressing on the control electrodes of said second mentioned valves a potential having a value less than the critical potentialmeans for introducing periodic potentials in the anode circuits of said second mentioned.

valves to render ineffective said positive potential and to prevent starting of said second mentioned valves during said predetermined intervals, means responsive to the current conducted by each of said first mentioned valves for impressing a positive potential on the control electrode of each of said valves to render said second mentioned valves conductive when said rst mentioned valves conduct at any time other than during said predetermined intervals, means respon' sive to an electrical condition of said second mentioned valves for introducing in the anode circuits of said second mentioned valves a potential for rendering ineffective said periodic potentials and for maintaining conductive one of said second mentioned valves comprising an electric valve of the vapor electric type for maintaining conductive said one of said second mentioned valves and means for interrupting the current through said one of said second mentioned valves.

2. In combination, electric transmitting apparatus including a group oi* main electric valves, means for rendering the electric valves conductive during diilerent predetermined intervals, and a circuit for indicating the nrst of said ectric valves to lose control including a plura ty of auxiliary electric valves each having an anode. a cathode and a control electrode and each being associated with a predetermined one of said main electric valves for energizing said circuit in response to abnormal operation of said main electric valves and comprising means common to all the auxiliary valves for introducing into the associated anode circuit of each oi' the auxiliary valves a potential tending to render the auxiliary valves. conductive, means i'or introducing into the anode circuits potentials to render the tlrst potential ineilective during at least a portion of the intervals of conduction of the associated main valve and means responsive to the current conducted by the main electric valves for impressing on the control electrodes potentials which tend to render the auxiliary valves conductive only when the associated main valves actually conduct current.

3. In combination, electric translating apparatus including a main electric valve, means for rendering said electric valve conductive during predetermined intervals, an electric circuit, an auxiliary electric valve for eiecting energization oi said circuit in response to abnormal operation oi said main electric valve and having an anode, a cathode and a control electrode, means for introducing into the anode circuit of the auxiliary electric valve a potential tending to render said auxiliary electric valve conductive, means for introducing in the anode circuit a potential tending to render the rst potential ineiective during said predetermined conducting intervals, and means responsive to the current conducted by the main valve to impress upon said control electrode a potential tending to render said auxiliary valve conductive only when the main valve actually conducts current.

4. In combination, an alternating current circuit, a load circuit, electric translating apparatus connected therebetween and including an electric valve, means for rendering said electric valve conductive during a predetermined fraction of half cycles of voltage of said alternating current circuit, a control circuit, an auxiliary electric valve for energizing said control circuit'in response to abnormal operation of said main electric valve and including an anode, a cathode and a control electrode, means for introducing into the anode circuit of said auxiliary electric valve a potential tending to render said auxiliary valve conductive, means for introducing into the anode 'circuit a potential of substantially peaked wave form to render the ilrst potential ineilective during at least a part of said fraction, and means comprising a magnetic saturable device responsive to the current conducted by the main electric valve for impressing on said control electrode a potential oi peaked wave form tending to render said auxiliary valve conductive only when the main valve actually conducts current.

5. In combination, electric translating apparatus including a main electric valve, means for rendering said electric valve conductive during predetermined intervals, a control circuit, an auxiliary electric valve for energizing said control circuit in response to abnormal operation of said main electric valve and comprising an anode, a

cathode and a control electrode, means for introducing into the anode circuit oi said auxiliary valve a potential tending to render the auxiliar! valve conductive, means for introducing into the anode circuit a periodic potential tending to render the first potential ineiiective during at least a portion oi said intervals, means responsive to the current conducted by the main valve tending to render the auxiliary valve conductive .only when the main valve actually conducts current. means for introducing into the anode circuit an additional potential after the auxiliary electric valve conducts current to maintain current through said auxiliary valve, and means i'or interrupting the current through the auxiliary electric valve.

6. In combination, an electric translating circuit including electric valve means.` a plurality oi circuits each associated with said valve means for indicating the occurrence ot iaults oi predetermined diiierent character, and means for indicating the ilrst of said indicating circuits to operate.

7. In combination, a plurality oi conductors, a group of electric valves each being associated with a predetermined one oi said conductors ior indicating the occurrence of a predetermined electrical condition of said. conductors, a second group of electric valves each being associated with a predetermined one of said conductors for indicating the occurrence of a different predetermined electrical condition of said conductors, and means for indicating the rst group ci said groups oi valves to operate.

8. In combination, a plurality oi.' conductors, a group of electric valves each being associated with apredetermined one of said conductors for indicating the occurrence of a predetermined electrical condition of said conductors. a second group of electric valves each being associated with a predetermined one of said conductors for indicating the occurrence o! a diilerent predetermined electrical condition of said conductors, and means for controlling the energization oi said conductors in response to the energization of any one of said groups oi valves.

9. In combination, an electric translating circuit including a group oi' electric valves each being arranged to conduct during predetermined intervals, an indicating circuit for indicating the first valve of said group to conduct at any time other than during said predetermined intervals, a second indicating circuit for indicating the first valve of said group to fail to conduct within said predetermined intervals, a third indicating circuit for indicating the ilrst valve of said group to be subject to a reverse current condition, and means for indicating the ilrst circuit of said indicating circuits to operate.

10. In combination, an electric translating circuit including a group oi' electric valves each being connected to conduct during predetermined intervals, an indicating circuit for indicating the first valve of said group to conduct at any time other than during said predetermined intervals, a second circuit for indicating the nrst valve of said group to fail to conduct within said predetermined intervals, a third circuit for indicating the ilrst valve of said group to be subjected to a reverse current condition, and means i'or controlling said electric translating circuit in response to the energization of one oi' said indicating circuits.

BURNICE D. BEDFORD. 

